Get a list (without nested list) directly from a list comprehension

Question

I want to return a list with the interleaved elements of two lists directly from the list comprehension - without use a next step to flaten the result. Is it possible?

alist1_temp=[1, 4,2]
alist2_temp=[3, 7,4]
t=[[x,y] for x,y in zip(alist1_temp, alist2_temp)]

Return [[1, 3], [4, 7],[2, 4]]

But how can I get directly from the list-comprehension [1, 3, 4, 7, 2, 4]?

Mehrdad Pedramfar · Accepted Answer · 2019-01-06T14:50:09.863

5

Try this with just zip to get it in that order that you want:

[i for j in zip(alist1_temp, alist2_temp) for i in j]

if you don't mind the order just do:

alist1_temp + alist2_temp

or get it with itertools.chain thanks to @buran:

import itertools

list(itertools.chain(alist1_temp, alist2_temp))

edited Jan 06 '19 at 14:50

answered Jan 06 '19 at 14:38

Mehrdad Pedramfar

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with the chain - why not just `list(itertools.chain(alist1_temp, alist2_temp))`? it's not comprehension, but I am not sure comprehension is strict requirement. And anyway the order of elements in the result is different. – buran Jan 06 '19 at 14:48
@buran Right, surely you are right – Mehrdad Pedramfar Jan 06 '19 at 14:49
@buran Edited, thanks for your comment – Mehrdad Pedramfar Jan 06 '19 at 14:50

score 1 · Answer 2 · answered Jan 06 '19 at 14:54

1

If you like numpy way of doing this, you could use this!

np.vstack((alist1_temp,alist2_temp)).flatten('F')

or you can flatten your list comprehension as well

np.array(t).flatten()

answered Jan 06 '19 at 14:54

Venkatachalam

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score 1 · Answer 3 · answered Jan 06 '19 at 15:14

As you specified that you want get it from from the list-comprehension:

alist1_temp=[1,4,2]
alist2_temp=[3,7,4]
L = len(alist1_temp)+len(alist2_temp)
t = [alist2_temp[i//2] if i%2 else alist1_temp[i//2] for i in range(L)]
print(t) #prints [1, 3, 4, 7, 2, 4]

Get a list (without nested list) directly from a list comprehension

3 Answers3